Field of the Invention
The present invention relates to an encoding module and related systems and components such as encoding elements, RFID printer-encoders, and access control systems.
Description of Related Art
Radio frequency identification (“RFID”) transponders, either active (e.g., battery-powered, -assisted, or -supported) or passive (e.g., RF field activated), are typically used with an RFID reader or similar device for communicating information back and forth. In order to communicate, an antenna of the reader exposes the transponder to a radio frequency (RF) electromagnetic field or signal. In the case of a passive UHF transponder, the RF electromagnetic field energizes the transponder and thereby enables the transponder to respond to the reader by re-radiating the received signal back and modulating the field in a well-known technique called backscattering. In the case of an active transponder, the transponder may respond to the electromagnetic field by transmitting an independently generated, self-powered reply signal to the reader.
Problems can occur when interrogating one targeted transponder surrounded by multiple adjacent transponders regardless on whether the transponders are field activated or independently powered by an internal energy source. For example, an interrogating electromagnetic signal may activate more than one transponder at a given time. This simultaneous activation of multiple transponders may lead to collision or communication errors because each of the multiple transponders may transmit reply signals to the reader at the same time.
The challenge of avoiding multiple and simultaneous transponder activation may be especially acute in some applications. RFID printer-encoders are one example. RFID printer-encoders are devices capable of encoding and printing a series or stream of labels with embedded transponders. A conveyor system is another example of an application in which undesirable multiple transponder activation may be acute.